High molecular weight linear polyesters and copolyesters of glycols and terephthalic or isophthalic acid have been available for a number of years. These are described inter alia in Whinfield et al., U.S. Pat. No. 2,465,319 and in Pengilly, U.S. Pat. No. 3,047,539. These patents disclose that the polyesters are particularly advantageous as film and fiber formers.
Such polyesters have not been widely accepted for use as molding resins, however, until only fairly recently, because of their relative brittleness in thick sections when crystallized from the melt. This problem was overcome by varying the crystal texture, e.g., by using two-step molding cycles or including nucleating agents, and by molecular weight control. This permitted the marketing of injection moldable poly(ethylene terephthalates) which typically, in comparison with other thermoplastics, offered a high degree of surface hardness and abrasion resistance, and lower surface friction.
Simultaneously with the development of injection molding grades of polyester resins, fiber glass reinforced compositions were also provided. See, Furukawa et al., U.S. Pat. No. 3,368,995 and Zimmerman et al., U.S. Pat. No. 3,814,725. These injection moldable compositions provided all of the advantages of unfilled polyesters and, also, because of the glass reinforcement had higher rigidity, yield strength, modulus and impact strength.
Pristine, or sizing free, glass fibers have been disclosed as reinforcing agents in Abeleen et al., U.S. Pat. No. 4,539,350 and Abeleen et al., U.S. Pat. No. 4,568,712. These two patents teach the addition of a polysiloxane compound to improve the ductility of the polyester resins.
Conventional starch based sizings have been disclosed in the prior art. Abolins, in U.S. Pat. No. 3,671,487, teaches the use of lightly sized or unsized glass fibers in preparing flame and drip retardant glass reinforced polyester resins. Wambach, in U.S. Pat. No. 4,113,692, employs conventional sized glass fibers and polycarbonate resins to increase resistance to warpage in poly(1,4-butylene terephthalate) and poly(ethylene terephthalate) resin blends. Similarly, warp resistant polyesters with glass filaments in combination with talc or mica fillers are disclosed in United Kingdom Patent Nos. 1,592,205 and 1,592,668, but sizings are conventional and are either optional or lightly employed.
Non-starch aqueous sizings for treating glass fibers are disclosed in Temple et al., U.S. Pat. No. 4,394,475. The patentee therein teaches a sizing composition comprising a non-starch film forming polymer, a polyethylene containing polymer and a wax which improves the slip/flow characteristics of the glass fibers.
Epoxy coated glass fibers to reinforce polymer materials are disclosed in Watson, U.S. Pat. No. 4,487,797 and Das et al., U.S. Pat. No. 4,745,028. Watson teaches an aqueous chemical composition comprising a water dispersible, emulsifiable or soluble epoxy novolac film forming polymer in combination with a glass fiber coupling agent and a poly(oxyalkylene-oxyethylene)polyol copolymer as the sizing agent. Das et al., teach a sizing composition which comprises an aqueous epoxy polyurethane with blocked isocyanate crosslinking groups and at least one or more organo coupling agents. Ogawa et al., U.S. Pat. No. 4,276,208 describe polyester resin compositions having glass fibers surface coated with an epoxy compound having at least two epoxy groups in the molecules such as bisphenol-A type epoxy compound, bisphenol-F type epoxy compound and novolac type epoxy compound, in combination with a salt of a montan wax.
It is further known to flame retard the polyester composition with a variety of flame retardant agents, including halogenated organic compounds and phosphorus compounds. However, it has recently been discovered that when halogenated bis-imide flame retardants are employed as the flame retardant agent in glass filled polyesters, there results a discoloration in the final polyester resin.
There is no teaching or suggestion in the prior art which contemplates the use of a certain epoxylated compounds or polyolefins as glass fiber coating agents to impart improved color on polyester resins which are flame retarded with a halogenated bis-imide. Unexpectedly, it has now been found that thermoplastic resin compositions comprising a polyester resin, a halogenated bis-imide flame retardant and a glass fiber reinforcing agent coated with a coating agent comprising epoxylyated phenolics, epoxylated carboxylic acids, polymers of unsaturated epoxides, epoxylated dienes or polyenes; or polyolefins suprisingly exhibit a marked improvement in color over flame retarded polyester resin compositions containing glass fibers coated with other coating agents of the prior art such as polyurethane. Further, the coated glass fibers of the present invention have excellent strand integrity making them especially suitable for use in the preparation of molding compositions.
Special mention is made of Delvin et al., U.S. Pat. No. 4,990,549 which teaches that polyesters flame retarded with any of the conventional flame retardant agents can be modified with a glass fiber reinforcing agent treated with a sizing agent comprising a di- or tri-functional cyanurate or isocyanurate to provide improved physical properties on the polyester resin. However, the sizing agents disclosed in Delvin et al. provide glass fibers with poor strand integrity and are only difficultly compounded into moldable compositions.